1. Field of the Invention
The present invention relates to a hydraulic control apparatus of an automatic transmission for a vehicle, and more particularly to a control technique of a motor driving type hydraulic pump constituting a hydraulic power source.
2. Description of the Related Art
As a related art, there has been known an automatic transmission for a vehicle provided with respective hydraulic actuators for switching a shift transmission, driving a lock-up mechanism, circulating to an oil cooler and the like. Further, the automatic transmission for the vehicle is provided with a hydraulic control apparatus for controlling the hydraulic actuators. There is a case that a so-called electric motor-driven type hydraulic pump in which the hydraulic pump functioning as a hydraulic power source of the hydraulic control apparatus is driven, for example, by an electric motor is used. A rotational speed of the electric motor-driven type hydraulic pump is determined to a required minimum level by being controlled by the hydraulic control apparatus with taking a required hydraulic pressure, a required flow amount including a leak amount, a pump efficiency and the like into consideration. Further, an electric power consumption and a noise of the electric motor is set to a required minimum level.
For example, in the hydraulic control apparatus described in Japanese Unexamined Patent Publication No. 2000-27992, there is shown a matter that a first pump for supplying a shift transmission control flow amount and an oil pump for supplying an oil cooler circulating flow amount are driven by the same motor. In particular, in this system, a flow amount supply corresponding to the requirement is achieved by controlling the motor rotational speed, so that the pump with the greater flow amount in two pumps can be always supplied. In accordance with this structure, there is an advantage that an oil pressure can be necessarily and sufficiently generated in an electrically driven vehicle, a hybrid car or the like traveling by a motor functioning as a prime mover.